1. Field of the Invention
The present invention relates to an image forming system comprising an image forming apparatus that prints an image on a sheet and a post processing apparatus that performs a post process such as stapling, punching, folding and etc. on a printed sheet, a post processing apparatus preferably used in the image forming system, a sheet feed control method, and a sheet feed control program.
2. Description of the Related Art
The following description sets forth the inventor's knowledge of related art and problems therein and should not be construed as an admission of knowledge in the prior art.
When an image forming apparatus sequentially prints images on a plurality of sheets, the sheets are individually fed from its sheet feed tray to its printer at a certain sheet interval, then discharged on its sheet discharge tray, which is generally known.
Meanwhile, if a post processing apparatus is connected to such an image forming apparatus and the post processing apparatus performs a post process on the plurality of printed sheets, the post processing apparatus needs a post process time from the start until the end of the post process. Thus, when the top sheet of a following job is fed at a certain sheet interval right after the last sheet of a job to be post-processed, the top sheet of a following job may happen to be fed to a post processing position in the post processing apparatus before a post process is completed, which is inconvenient.
To cope with this issue, an art is disclosed wherein the start of feeding the top sheet of a following job is delayed by a certain fixed time that is required to perform a post process on a job.
Generally, a post process time is changeable depending on a sheet size, a process condition and etc. However, according to the art disclosed in Japanese Unexamined Laid-open Patent Publication No. 11-208979, feeding the top sheet of a following job is delayed by a fixed time, not by an appropriate time adjusted for each job depending on its post process time, which is not very productive.
Further, to cope with this issue, an art is disclosed in Japanese Unexamined Laid-open Patent Publication No. 2006-256710, wherein a process time (T1) and a discharge time (T2) are calculated based on a sheet size and a process condition of a job currently post-processed, and a sheet accumulation time (sheet feed time) calculated based on a sheet size and the number of sheets of a following job, is subtracted from T1+T2 to obtain a job wait time (Ta), and then feeding the top sheet of the following job is delayed by Ta.
With this art disclosed in Japanese Unexamined Laid-open Patent Publication No. 2006-256710, the top sheet of a following job is fed depending on a post process time of a previous job. However, there is still an issue with this art as below.
In order to perform a post process, the post processing apparatus needs preparation. For example, if stapling is performed as a post process, its stapler has to move to an appropriate position to meet a stapling position on sheets, which is specified by a user, and when its stapler finishes moving to an appropriate position, the post processing apparatus can perform a post process. If such preparation is finished before the last sheet of a job to be post-processed arrives at a post processing position, the post processing apparatus would successfully executes the job simply by delaying feeding the top sheet of a following job by a job waiting time (Ta), since the post processing apparatus immediately performs a post process as soon as the last sheet of the job arrives at the post processing position. On the other hand, if such preparation is not finished before the last sheet of a job to be post-processed arrives at a post processing position, the post processing apparatus would not successfully execute the job only by delaying feeding the top sheet of a following job by a job waiting time (Ta), since the top sheet of a following job may happen to be fed to the post processing position before the post processing apparatus completes a post process on the previous job.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. Indeed, certain features of the invention may be capable of overcoming certain disadvantages, while still retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.